This invention relates to pyridinium derivatives useful as medicines. More specifically, the present invention relates to compounds useful as antagonists of the platelet activating factor (PAF), the compounds being represented by the following formula: ##STR10## wherein ##STR11## stands for an optionally substituted pyridinium ring; R.sup.1 stands for a lower alkyl group or aralkyl group; R.sup.7 and R.sup.10 each stand for hydrogen, a lower alkyl group, aryl group or aralkyl group; l denotes 0 or 1; R.sup.5 stands for a phenylene group or an alkylene group which may be substituted; R.sup.11 stands for an alkyl group or an aryl group; X stands for a group of the formula --CH.sub.2 OCH.sub.2 -- or a group of the formula ##STR12## (wherein R.sup.6 stands for hydrogen, a lower alkyl or a lower alkoxy, and m denotes an integer of 0 to 3); U stands for a group of the formula ##STR13## (wherein R.sup.4 stands for hydrogen, a lower alkyl group, aryl group or aralkyl group); Y and Z each stand for a divalent chain group consisting of one to six members which are selected from the class consisting of groups of the formulae --O--, ##STR14## --CO--, --S-- and --SO.sub.2 -- (wherein R stands for hydrogen, a lower alkyl group, acyl group or aryl group) and at least one of which is a group of the formula --O-- or ##STR15## with the proviso that the R groups may be the same or different from each other, or may form a ring together when two or more groups of the formula ##STR16## are contained, that R may be bonded to R.sup.4 when Y contains a group of the formula ##STR17## and that R may be bonded to R.sup.11 when Z contains a group of the formula ##STR18## and W.sup..crclbar. stands for a counter anion.
PAF has a phospholipid structure and is a chemical transmitter existing in a living body. It has been made clear that PAF is, in a living body, closely concerned with allergy, anaphylaxis, inflammation, etc. and it is also known that PAF has a strong hypotensive activity and platelet agglutinating activity. On administering PAF to an animal, the animal may, in some cases, be killed from shock. Symptoms caused by the shock from PAF have much resemblance to those caused by the shock from endotoxin, and it has been demonstrated that PAF is concerned with the endotoxin shock.
On the other hand, while a variety of compounds having PAF-antagonistic activity are known, very few of them are satisfactory in PAF-antagonistic activity in a living body. And, even when the PAF-antagonistic activity in a living body is satisfactory, not a few of those compounds have some restrictions in the administration method.